The present invention relates to a method and apparatus for efficient high volume pumping of neutral gas from a chamber to produce a vacuum by ionizing the neutral gas with a plasma and providing magnetic field lines for the ions to flow through the apparatus.
It is well-known in the prior art that a plasma, defined herein as a space-charge neutral ion electron gas of selected density, may be used in a variety of applications including accelerators, mass spectrometers, high temperature chemical reactors, vapor deposition devices and in controlled thermonuclear reactions such as may be carried out, for example, in tokamak reactors.
Many applications of vacuum technology require a high gas pumping rate with a minimum of contamination by foreign materials such as oil and a low pressure operating environment. The efficiency with which high vacuums can be maintained in the presence of high gas throughput is critical in applications such as large volume magnetic fusion devices and in other applications of the type summarized above. There has also been found to exist a need, particularly in magnetic fusion devices, for such a vacuum pump to function in the proximity of high temperature fusion plasma with a minimum of contamination of the fusion plasma itself.
A number of vacuum pumping devices and methods have been disclosed in the prior art generally of a type contemplated by the present invention. For example, reference is made to U.S. Pat. No. 3,160,566 issued Dec. 8, 1964 to R. A. Dandl et al for a plasma generator having certain structural similarities to that disclosed in the present invention.
In particular, the above-noted reference disclosed a method and apparatus for producing a stable, medium density, high temperature plasma in an evacuated enclosure permeated by a suitable magnetic field wherein the plasma was shielded from neutral gas particles by an energetic plasma blanket. The blanket was created by connecting a microwave generator to a reflecting cavity within the evacuated enclosure so that the electrons therein were heated at the electron cyclotron frequency of the electrons. The heated electrons were in turn caused to produce ions with both the ions and electrons moving along the magnetic field lines to produce the plasma blanket. The plasma blanket developed by the method and apparatus of the above-noted reference was intended to essentially eliminate charge-exchange losses of the plasma within the inside of the blanket while providing a background for dissociation, ionization, etc., for trapping and for providing a means for optimizing the electron temperature for stability.
The method and apparatus of the above-noted reference includes certain basic features in common with the method and apparatus of the present invention. Accordingly, the above-noted reference, U.S. Pat. No. 3,160,566, is incorporated herein as though set forth in its entirety to permit a better understanding of the present invention.
Even with prior art vacuum devices of the type disclosed by the above-noted reference, there has been found to remain a need for more effective vacuum pumping techniques for achieving efficient high volume pumping of neutral gas from a chamber to produce a vacuum by ionizing the neutral gas with a plasma and providing magnetic field lines for the ions to flow through the vacuum pumping apparatus.